Requests for transmission parameters in a multi-user scenario

ABSTRACT

Link adaptation is supported in a multi-user MIMO environment. In some aspects, a frame including a transmission parameter request (e.g., a null data packet announcement (NDPA) including a modulation and coding scheme (MCS) request (MRQ)) specifies multiple destinations. In some aspects, a decision to transmit a frame specifying multiple destinations is based on whether all of destinations support providing feedback to such a frame. In some aspects, transmission parameter feedback (e.g., MCS feedback (MFB)) including channel estimate information is provided in a case where MFB of type MU is requested.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to concurrently filed and commonly ownedU.S. patent application Ser. No. ______, entitled “VERIFYING SUPPORT FORREQUESTS FOR TRANSMISSION PARAMETERS IN A MULTI-USER SCENARIO,” andassigned Attorney Docket No. 111604U2; and U.S. patent application Ser.No. ______, entitled “PROVIDING TRANSMISSION PARAMETERS FOR MULTI-USERCOMMUNICATION,” and assigned Attorney Docket No. 111604U3; thedisclosure of each of which is hereby incorporated by reference herein.

BACKGROUND

1. Field

This application relates generally to wireless communication and morespecifically, but not exclusively, to link adaptation for multi-userwireless communication.

2. Introduction

In some types of multiple access wireless communication systems, anaccess point (e.g., a base station) provides network connectivity andother services for access terminals (e.g., cell phones, computers, etc.)in the vicinity of the access point. In some cases, the access point maycommunicate using a single-user (SU) mode (e.g., using beamforming tocommunicate with a given access terminal) or using a multi-user (MU)mode (e.g., using multi-user multiple input multiple output (MU-MIMO) toconcurrently communicate with several access terminals).

A MU-MIMO mode of operation may be used to enable concurrentcommunication between an access point and multiple access terminals. Forexample, in an IEEE 802.11ac compliant system, an 802.11ac base stationmay employ MU-MIMO to communicate with several stations. An access pointof a MIMO system employs multiple antennas for data transmission andreception while each access terminal employs one or more antennas. Theaccess point communicates with the access terminals via forward linkchannels and reverse link channels. A forward link (or downlink) channelrefers to a communication channel from a transmit antenna of the accesspoint to a receive antenna of an access terminal, and a reverse link (oruplink) channel refers to a communication channel from a transmitantenna of an access terminal to a receive antenna of the access point.

MIMO channels corresponding to transmissions from a set of transmitantennas to a receive antenna are referred to spatial streams sinceprecoding (e.g., beamforming) is employed to direct the transmissionstoward the receive antenna. Consequently, in some aspects each spatialstream corresponds to at least one dimension. A MIMO system providesimproved performance (e.g., higher throughput and/or greaterreliability) through the use of the additional dimensionalities providedby these spatial streams.

The quality of the channel between the access point and each of theaccess terminals is generally taken into account when selectingtransmission parameters (e.g., modulation and coding scheme (MCS)) fortransmissions from the access point to the access terminals. Forexample, the access point may send a training sequence to the accessterminals, and request each access terminal to provide feedbackincluding a channel estimate derived from the training sequence and atransmission parameter estimate that is based on that channel estimate.The access point may then use these transmission parameter estimates tocontrol subsequent transmissions to the access terminals. As a specificexample, an 802.11 base station broadcasts a null data packetannouncement (NDPA) frame including an MCS request (MRQ), followed bythe null data packet (NDP). A station responds to this request with MCSfeedback (MFB). To support such a link adaptation scheme, variousspecifications have been defined for managing the transmissionparameters.

For example, under 802.11, if MFB is sent in the same PLCP Protocol DataUnit (PPDU) as a Very High Throughput Compressed Beamforming (VHT-CB)frame of type SU, the MFB responder shall estimate the recommended MFBunder the assumption that the MFB requester will use the steeringmatrices (e.g., channel estimate) indicated by the VHT-CB frame. Also,if the MFB requester sends the MRQ in an NDPA requesting SU-beamformingfeedback, then the MFB responder shall include the corresponding MFBfeedback in the response VHT-CB frame.

While the above specifications address SU mode, these specifications donot address link adaptation for MU mode. Accordingly, there is a needfor effective techniques for providing link adaptation for MU mode.

SUMMARY

A summary of several sample aspects of the disclosure follows. Thissummary is provided for the convenience of the reader and does notwholly define the breadth of the disclosure. For convenience, the termsome aspects is used herein to refer to a single aspect or multipleaspects of the disclosure.

The disclosure relates in some aspects to link adaptation in an MUenvironment. For example, in an 802.11-based system, link adaptation issupported in a case where an NDPA specifies multiple destinations (e.g.,stations) and/or where MFB of type MU is requested.

The disclosure relates in some aspects to a link adaptation request thatis included in a frame directed to multiple destinations. For example,an access point may transmit a frame that includes a feedback request(e.g., an MRQ in an NDPA) and that identifies multiple stations. In thiscase, all of the stations identified in the frame may provide therequested feedback at some point in time. Accordingly, in some aspects,a wireless communication scheme in accordance with the teachings hereinmay involve: receiving a frame at a first apparatus, wherein the framecomprises a request for at least one transmission parameter and furthercomprises identifiers of a plurality of apparatuses; determining thatthe first apparatus is identified by one of the identifiers; andtransmitting the requested at least one transmission parameter as aresult of the determination.

The disclosure relates in some aspects to allowing a frame thatidentifies multiple destinations to include a feedback request only wheneach of these destinations has indicated that providing such feedback iscurrently supported. For example, in some aspects, such a request is notsent if any one of the recipients is unable to decode the frameincluding the request. Accordingly, in some aspects, a wirelesscommunication scheme in accordance with the teachings herein mayinvolve: determining whether each apparatus of a plurality ofapparatuses has indicated that responses will be provided to requestsfor at least one transmission parameter; and transmitting a frame as aresult of the determination, wherein the frame comprises a request forthe at least one transmission parameter from the plurality ofapparatuses and further comprises identifiers of the plurality ofapparatuses.

The disclosure relates in some aspects to defining the meaning of a linkadaptation response that is included in the same frame as a channelestimation report. For example, when a station is responding to afeedback request with an MU channel estimate, the station may provide atransmission parameter estimate that is generated assuming that thatchannel estimate will be used for a SU transmission. Accordingly, insome aspects, a wireless communication scheme in accordance with theteachings herein may involve: estimating at least one transmissionparameter for single-user beamformed transmission based on a channelestimate for multi-user transmission by an apparatus; generating a frameincluding the channel estimate and the at least one transmissionparameter; and transmitting the frame to the apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other sample aspects of the disclosure will be described inthe detailed description and the claims that follow, and in theaccompanying drawings, wherein:

FIG. 1 is a simplified block diagram of several sample aspects of awireless communication system configured to support link adaption in anMU environment in accordance with the teachings herein;

FIG. 2 is a simplified diagram of sample MU-MIMO transmissions;

FIG. 3 is a simplified diagram of frames that may be employed in802.11ac in accordance with the teachings herein;

FIG. 4 is a flowchart of several sample aspects of operations performedin conjunction with the use of a frame that comprises a transmissionparameter request and that identifies multiple destinations inaccordance with the teachings herein;

FIG. 5 is a flowchart of several sample aspects of operations performedin conjunction with controlling whether to transmit a frame thatcomprises a transmission parameter request and that identifies multipledestinations in accordance with the teachings herein;

FIG. 6 is a flowchart of several sample aspects of operations performedin conjunction with generating a frame including a channel estimate inaccordance with the teachings herein;

FIG. 7 is a simplified block diagram of several sample aspects ofcomponents that may be employed in communication nodes in accordancewith the teachings herein;

FIG. 8 is a simplified block diagram of several sample aspects ofcommunication components; and

FIGS. 9-11 are simplified block diagrams of several sample aspects ofapparatuses configured to support link adaption in accordance with theteachings herein.

In accordance with common practice, the features illustrated in thedrawings are simplified for clarity and are generally not drawn toscale. That is, the dimensions and spacing of these features areexpanded or reduced for clarity in most cases. In addition, for purposesof illustration, the drawings generally do not depict all of thecomponents that are typically employed in a given apparatus (e.g.,device) or method. Finally, like reference numerals may be used todenote like features throughout the specification and figures.

DETAILED DESCRIPTION

Various aspects of the disclosure are described below. It should beapparent that the teachings herein may be embodied in a wide variety offorms and that any specific structure, function, or both being disclosedherein is merely representative. Based on the teachings herein oneskilled in the art should appreciate that an aspect disclosed herein maybe implemented independently of any other aspects and that two or moreof these aspects may be combined in various ways. For example, anapparatus may be implemented or a method may be practiced using anynumber of the aspects set forth herein. In addition, such an apparatusmay be implemented or such a method may be practiced using otherstructure, functionality, or structure and functionality in addition toor other than one or more of the aspects set forth herein. Furthermore,an aspect may comprise at least one element of a claim. As an example ofthe above, in some aspects, an apparatus for wireless communicationcomprises: a transceiver configured to receive a frame, wherein theframe comprises a request for at least one transmission parameter andfurther comprises identifiers of a plurality of apparatuses; and aprocessing system configured to determine that the apparatus isidentified by one of the identifiers, wherein the transceiver is furtherconfigured to transmit the requested at least one transmission parameteras a result of the determination. Moreover, in some aspects, the framecomprises a null data packet announcement (NDPA) frame.

FIG. 1 illustrates sample aspects of a wireless local area network(WLAN) 100 where an access point 102 including a MU-MIMO transceiver 104communicates with an access terminal 106 and an access terminal 108. Theaccess terminals 106 and 108 represent wireless communication devices(e.g., 802.11ac devices) that may be referred to as users, stations,destinations, user equipment, user devices, clients, and so on invarious implementations. Each of the access terminals 106 and 108includes a transceiver 122 and 124, respectively, for communicating withthe access point 102. In this example, the access point 102 includes twotransmit antennas 110 and 112, the access terminal 106 includes onereceive antenna 114, and the access terminal 108 includes one receiveantenna 116.

The MU-MIMO transceiver 104 employs precoding (e.g., beamforming) fortransmissions via the antennas 110 and 112 such that a spatial stream118 (as represented in simplified form by a corresponding dashed line)is directed to the access terminal 106 and a spatial stream 120 (again,represented by a corresponding dashed line) is directed to the accessterminal 108. It should be appreciated that the teachings herein areapplicable to other implementations that include a different number oftransmit antennas, a different number of receive antennas, a differentnumber of access terminals, and a different number of spatial streams.

FIG. 2 illustrates a simplified example of signal transmission from theaccess point for the case where there are two access terminals. Here, asin the example of FIG. 1, two transmit antennas are used to sendinformation to the two access terminals, each of which has a singlereceive antenna. As represented by the matrix 202, the access pointgenerates an output signal x(1,n) destined for the first access terminaland generates an output signal x(2,n) destined for the second accessterminal. The parameter n represents that the signals are sent over ntones using orthogonal frequency-division multiplexing (OFDM). Theoutput signals are applied to a precoding matrix 204 (e.g., withelements P₁₁, P₁₂, P₂₁, and P₂₂ for a 2×2 matrix. The result of thisoperation is transmitted via two antennas 206. The resulting signals aretransmitted via a channel matrix H(n) to the receive antennas 208, wherethe channels associated with the different transmit antenna-receiveantenna pairs are represented by h₁₁, h₁₂, h₂₁, and h₂₂ as shown. Thereceived signals are represented by a matrix 210 where, as stated above,one receive antenna is associated with each access terminal. Here, thesignal y₁(n) is the signal received at one access terminal and thesignal y₂(n) is the signal received at the other access terminal. Asmentioned above, in some aspects, link adaptation involves determiningwhich transmission parameters (e.g., MCS) are to be used fortransmissions over the channels between the access point and the accessterminals.

In accordance with the teachings herein, link adaptation is supportedfor an MU environment through the definition of certain informationfields in frames and actions to be taken when using such frames. FIG. 3illustrates several examples of frames that may be employed in 802.11acto support MU link adaptation. In this example, a base station (BS)broadcasts an NDPA and a NDP, and each station (STA) transmits a VHT-CBframe.

The NDPA frame of FIG. 3 comprises PHY and MAC sections. The MAC sectionincludes a header and a payload. The header includes a highthroughput/very high throughput control (HT/VHT CTL) field. As indicatedby the HT/VHT nomenclature used herein, this control field has twoforms: a high throughput (HT) variant and a very high throughput (VHT)variant. This disclosure is primarily directed to the VHT variant. TheMRQ field of the HT/VHT control field is set equal to 1 to indicate thatMCS feedback is being requested. The payload includes stationinformation (STA Info) fields. In accordance with the teachings herein,the STA Info fields identify multiple destination stations. In theexample of FIG. 3, the association identifier (AID) fields in thedifferent STA Info fields will include identifiers for differentstations. For example, the identifiers may comprise local addresses ofthe stations or some other suitable identifiers. Each STA Info fieldalso includes a feedback type field that may be set to SU or MU. Thefeedback type fields refer the type of channel information that is to besent back. In the example of FIG. 3, these fields are set to MU.

The VHT-CB frame also comprises PHY and MAC sections, where the MACsection includes a header and a payload. This header also includes anHT/VHT control field. In this case, the HT/VHT control field includes anMFB field that the station uses to send back the requested MCS, etc. Inthose scenarios where the station provides a channel estimate with theMFB, this channel estimate is included in the payload of the VHT-CBframe.

In accordance with one aspect of the disclosure, an MRQ is allowed in anNDPA with multiple STA Info fields as depicted in FIG. 3. As discussedin more detail below, this is allowed as long as all of the stationslisted in the NDPA support the reception of an MRQ. The MRQ is intendedto solicit an MFB response from all of the stations listed in the NDPA.Each of these stations shall then reply with MFB in the VHT-CB reportframe. The above scheme may be used when either MU or SU type offeedback is specified in the NDPA.

In an alternative aspect, an NDPA with an MRQ may instead be defined assoliciting a response only from the first station listed in the NDPA. Inthis case, responses from the remaining stations may be obtained, forexample, by polling the remaining stations at a later point in time.

Thus, for an 802.11 environment, in the case of an NDPA frame withmultiple STA Info fields and carrying a VHT format of HT Control fieldwith MRQ set to 1, the MRQ is intended to solicit an MFB response fromall (or, some aspects, the first one of) the STAs listed in the AIDfield of the STA Info fields. In addition, an NDPA frame with multipleSTA Info fields shall not carry a VHT format of HT Control field withMRQ set to 1, unless all the STAs listed in the AID field of the STAInfo fields have advertized support for the solicited link adaptation.In other words, MRQ shall not be sent to STAs that have not set a VHTLink Adaptation Capable subfield in the most recently transmitted VHTCapabilities Info field of the VHT Capabilities element to a value thatindicates that solicited link adaptation is supported. In some aspects,such a value indicates that a STA supports “both” solicited andunsolicited link adaptation.

In the event the transmission of an NDPA including an MRQ and listingmultiple STA Info fields is not allowed, the transmitter (e.g., the basestation) will decide between using multi-station NDPA or requesting linkadaptation. That is, in this case, these two operations are notperformed at the same time.

In accordance with another aspect of the disclosure, in a scenario whereMU feedback is requested, a station may respond with SU feedback. Here,it should be appreciated that during sounding for an MU scenario, anaccurate estimation of the MU MCS is not obtained from a single one ofthe stations. Nevertheless, information regarding the status of a linkmay still be useful for MU rate prediction. For example, an MFB computedassuming SU beamforming may be leveraged to improve the rate selectionfor the MU-MIMO case, with the appropriate interpretation (e.g., thefeedback from different stations may provide an indication of relativerates to be used for the MU-based transmissions to these stations).Moreover, MU feedback may be used for SU beamforming (e.g., where, forthe MFB, it is assumed that SU beamforming is correct).

Thus, in accordance with the teachings herein, SU feedback may be sentfor an MU feedback request (e.g., an NDPA where the STA Info feedbacktype field is set to MU). If the MFB is sent in the same PPDU as aVHT-CB frame (e.g., of type MU, or even type SU), the MFB respondershall estimate the recommended MFB under the assumption that the MFBrequester (receiver) will use the steering matrices contained thereinfor performing a SU beamformed transmission.

Various advantages may be achieved through the use of such a scheme. Insome aspects, the response to SU and MU requests may be identical. Insome aspects, MU feedback may be used for SU beamforming as well. Such ascheme may provide improved rate adaption for MU.

With the above in mind, FIGS. 4-6 illustrate sample operations that maybe performed to provide MU link adaptation in accordance with theteachings herein. For purposes of illustration, the operations of FIGS.4-6 (or any other operations discussed or taught herein) may bedescribed as being performed by specific components. These operationsmay be performed by other types of components and may be performed usinga different number of components in other implementations. Also, itshould be appreciated that one or more of the operations describedherein may not be employed in a given implementation. For example, oneentity may perform a subset of the operations and pass the result ofthose operations to another entity.

FIG. 4 is directed to operations that are performed at a first apparatusthat receives a frame that requests at least one transmission parameterand that identifies multiple destinations. In some aspects, theseoperations are performed by an 802.11ac station.

As represented by block 402 of FIG. 4, at some point in time, a firstapparatus receives a frame. For example, a station may receive an NDPAframe from a nearby BS whereby, in some aspects, the NDPA serves toindicate that a null data packet will follow. Here, the received framecomprises a request for at least one transmission parameter and alsocomprises identifiers of a plurality of apparatuses. For example, asdiscussed above, the request may comprise an HT control field with MRQbit set to 1, and the identifiers (e.g., AIDs) may be included in STAInfo fields of the frame.

As represented by block 404, a determination is made as to whether thefirst apparatus is identified by one of the identifiers. For example, astation may determine that it is listed in an AID field of one of theSTA Info fields.

As represented by block 406, the first apparatus may also receive a nulldata packet from a second apparatus (e.g., the base station) thattransmitted the frame received at block 402. In some aspects, the nulldata packet comprises a training sequence that may be used to sound areceiver to enable the receiver to estimate a channel between atransmitter (e.g., a base station) and the receiver (e.g., a station).

In this case, as represented by block 408, the first apparatusdetermines at least transmission parameter (e.g., MCS) based on thereceived null data packet. For example, the first apparatus may estimatea channel between the first and second apparatuses, and generate thetransmission parameter(s) based on the estimate of the channel.

As represented by block 410, as a result of the determination of block404, the first apparatus transmits the at least one transmissionparameter. For example, a station may transmit transmission parametersto a base station via an MFB response (e.g., via a VHT-CB frame).

A transmission parameter may take various forms in accordance with theteachings herein. In general, as used herein, a transmission parameterspecifies how information is transmitted over a wireless medium. This isin contrast to, for example, a measured characteristic of a channel(e.g., a channel quality indication (CQI). Examples of transmissionparameters include, without limitation, modulation and coding scheme(e.g., 64 QAM, etc.), type of coding, number of spatial streams, targetbandwidth, minimum bandwidth, maximum bandwidth, target signal to noiseratio (SNR), minimum SNR, maximum SNR, and so on.

FIG. 5 is directed to operations that are performed in conjunction withcontrolling whether to transmit a frame that requests at least onetransmission parameter and that identifies multiple destinations. Insome aspects, these operations are performed by an 802.11ac basestation.

As represented by block 502, a determination is made as to whether eachapparatus of a plurality of apparatuses has indicated that responseswill be provided to requests for at least one transmission parameter.For example, as discussed above, a base station may determine, for eachof a set of stations, whether a Link Adaptation Capable subfield in avery high throughput (VHT) Capabilities Info field of a VHT Capabilitieselement that was most recently transmitted by the station is set to avalue that indicates support for solicited link adaptation (e.g., avalue indicating that “Both” solicited and unsolicited link adaptationis supported).

As represented by block 504, as a result of the determination of block502, the frame is transmitted. Continuing with the above example, ifeach of the stations has indicated that responses will be provided, thebase station will broadcast the frame (e.g., an NDPA frame).

Here, the frame comprises a request for the at least one transmissionparameter from the plurality of apparatuses along with identifiers ofthe plurality of apparatuses. For example, the request may comprise anMRQ and the frame may include STA Info fields as discussed herein.

As represented by block 506, as a result of transmitting the frame atblock 504, at least one transmission parameter is received from theplurality of apparatuses. For example, a base station may receive aVHT-CB frame from each of the stations identified at block 502.

As represented by block 508, the received transmission parameter(s)is/are used to conduct at least one transmission to the plurality ofapparatuses. For example, the base station may use received MCSinformation for MU-MIMO transmissions (e.g. to determine how muchtransmit power to use for each channel). As discussed above, eachstation may provide this MCS information based on a respective estimateof a channel from the base station to that station.

FIG. 6 is directed to operations that are performed in conjunction withtransmitting transmission parameter feedback in response to a feedbackrequest that specifies MU mode. In some aspects, these operations areperformed by an 802.11ac station.

As represented by block 602, at some point in time, an NDPA frame with acompressed channel feedback type set to MU beamforming may be received.For example, a station may receive an NDPA frame from a nearby basestation as discussed above.

As represented by block 604, at least one transmission parameter for SUbeamformed transmission is estimated based on a channel estimate for MUtransmission by an apparatus. For example, a station may generate achannel estimate for an MU transmission to be conducted by a basestation based on a null data packet received from the base station. Thestation may then estimate at least one transmission parameter (e.g.,MCS, number of spatial streams, etc.) based on the channel estimate.Here, the transmission parameter is estimated for SU beamformedtransmission even though the compressed channel feedback type is set toMU.

As represented by block 606, a frame including the channel estimate andthe at least one transmission parameter estimated at block 604 isgenerated. For example, a station may generate a data set to betransmitted as a VHT-CB frame and store the data set in a memory device(e.g., of a wireless transceiver).

As represented by block 608, the frame including the at least onetransmission parameter and the channel estimate (e.g., compressedsteering matrices) is transmitted. For example, the station may transmitthe data from the data set (e.g., after encoding, etc.) in the order andwith the timing specified for the frame (e.g., a packet). Thus, in an802.11 environment, a station may transmit a VHT-CB frame to a basestation at block 608.

FIG. 7 illustrates several sample components (represented bycorresponding blocks) that are incorporated into an apparatus to providefunctionality as taught herein. For purposes of illustration thesecomponents will be described in the context of a wireless node 702. Itshould be appreciated, however, that these components may be implementedin different types of apparatuses in different implementations (e.g., inan ASIC, in a system on a chip (SoC), etc.). In some aspects, thewireless node 702 represents an access terminal (e.g., corresponding toeach of the access terminals 106 and 108 of FIG. 1). In some aspects,the wireless node 702 represents an access point (e.g., corresponding tothe access point 102 of FIG. 1). The wireless node 702 may representanother type of device in other aspects. The components described inFIG. 7 may be incorporated into other nodes in a communication system.Also, a given node may contain one or more of the described components.For example, a wireless node may contain multiple transceiver componentsthat enable the wireless node to operate on multiple carriers and/orcommunicate via different technologies.

As shown in FIG. 7, the wireless node 702 includes one or moretransceivers (as represented by a transceiver 704) for communicatingwith other nodes. Each transceiver 704 includes a transmitter 706 fortransmitting signals (e.g., parameters, frames, packets, and otherinformation) and a receiver 708 for receiving signals (e.g., parameters,frames, packets, and other information).

The wireless node 702 also includes other components that are used inconjunction with the MU link adaptation operations as taught herein. Forexample, the wireless node 702 includes a processing system 710 forprocessing received signals and/or signals to be transmitted (e.g.,making determinations, generating frames, estimating transmissionparameters, including transmission parameters in frames, and so on) andfor providing other related functionality as taught herein. The wirelessnode 702 includes a memory component 712 (e.g., including a memorydevice) for maintaining information (e.g., parameters, frame data, andso on). The wireless node 702 also includes a user interface 714 forproviding indications (e.g., audible and/or visual indications) to auser and/or for receiving user input (e.g., upon user actuation of asensing device such a microphone, a camera, a keypad, and so on).

The components of FIG. 7 may be implemented in various ways. In someimplementations the components of FIG. 7 are implemented in one or morecircuits such as, for example, one or more processors and/or one or moreASICs (which may include one or more processors). Here, each circuit(e.g., processor) may use and/or incorporate memory for storinginformation or executable code used by the circuit to provide thisfunctionality. For example, some of the functionality represented byblock 704 and some or all of the functionality represented by blocks710-714 may be implemented by a processor or processors of a wirelessnode and memory of the wireless node (e.g., by execution of appropriatecode and/or by appropriate configuration of processor components).

FIG. 8 illustrates in more detail sample components that may be employedin a pair of wireless nodes of a MIMO system 800. In this example, thewireless nodes are labeled as a wireless device 810 (e.g., an accesspoint) and a wireless device 850 (e.g., an access terminal). It shouldbe appreciated that a MU-MIMO system will include other devices (e.g.,access terminals) similar to the wireless device 850. To reduce thecomplexity of FIG. 8, however, only one such device is shown.

The MIMO system 800 employs multiple (N_(T)) transmit antennas andmultiple (N_(R)) receive antennas for data transmission. A MIMO channelformed by the N_(T) transmit and N_(R) receive antennas is decomposedinto N_(S) independent channels, which are also referred to as spatialchannels, where N_(S)≦min{N_(T), N_(R)}.

The MIMO system 800 supports time division duplex (TDD) and/or frequencydivision duplex (FDD). In a TDD system, the forward and reverse linktransmissions are on the same frequency region so that the reciprocityprinciple allows the estimation of the forward link channel from thereverse link channel. This enables the access point to extract transmitbeamforming gain on the forward link when multiple antennas areavailable at the access point.

Referring initially to the device 810, traffic data for a number of datastreams is provided from a data source 812 to a transmit (TX) dataprocessor 814. Each data stream is then transmitted over a respectivetransmit antenna.

The TX data processor 814 formats, codes, and interleaves the trafficdata for each data stream based on a particular coding scheme selectedfor that data stream to provide coded data. The coded data for each datastream is multiplexed with pilot data using OFDM techniques or othersuitable techniques. The pilot data is typically a known data patternthat is processed in a known manner and used at the receiver system toestimate the channel response. The multiplexed pilot and coded data foreach data stream is then modulated (i.e., symbol mapped) based on aparticular modulation scheme (e.g., BPSK, QSPK, M-PSK, or M-QAM)selected for that data stream to provide modulation symbols. The datarate, coding, and modulation for each data stream are typicallydetermined by instructions performed by a processor 830. A memory 832stores program code, data, and other information used by the processor830 or other components of the device 810.

The modulation symbols for all data streams are then provided to a TXMIMO processor 820, which further processes the modulation symbols(e.g., for OFDM). The TX MIMO processor 820 then provides N_(T)modulation symbol streams to N_(T) transceivers (XCVR) 822A through822T. In some aspects, the TX MIMO processor 820 applies beam-formingweights to the symbols of the data streams and to the antenna from whichthe symbol is being transmitted.

Each transceiver 822 receives and processes a respective symbol streamto provide one or more analog signals, and further conditions (e.g.,amplifies, filters, and upconverts) the analog signals to provide amodulated signal suitable for transmission over the MIMO channel. N_(T)modulated signals from transceivers 822A through 822T are thentransmitted from N_(T) antennas 824A through 824T, respectively.

At the device 850, the transmitted modulated signals are received byN_(R) antennas 852A through 852R and the received signal from eachantenna 852 is provided to a respective transceiver (XCVR) 854A through854R. Each transceiver 854 conditions (e.g., filters, amplifies, anddownconverts) a respective received signal, digitizes the conditionedsignal to provide samples, and further processes the samples to providea corresponding “received” symbol stream.

A receive (RX) data processor 860 then receives and processes the N_(R)received symbol streams from N_(R) transceivers 854 based on aparticular receiver processing technique to provide N_(T) “detected”symbol streams. The RX data processor 860 then demodulates,deinterleaves, and decodes each detected symbol stream to recover thetraffic data for the data stream. The processing by the RX dataprocessor 860 is complementary to that performed by the TX MIMOprocessor 820 and the TX data processor 814 at the device 810.

A processor 870 periodically determines which precoding matrix to use(discussed below). The processor 870 formulates a reverse link messagecomprising a matrix index portion and a rank value portion. A memory 872stores program code, data, and other information used by the processor870 or other components of the device 850.

The reverse link message comprises various types of informationregarding the communication link and/or the received data stream. Thereverse link message is processed by a TX data processor 838, which alsoreceives traffic data for a number of data streams from a data source836, modulated by a modulator 880, conditioned by the transceivers 854Athrough 854R, and transmitted back to the device 810.

At the device 810, the modulated signals from the device 850 arereceived by the antennas 824, conditioned by the transceivers 822,demodulated by a demodulator (DEMOD) 840, and processed by a RX dataprocessor 842 to extract the reverse link message transmitted by thedevice 850. The processor 830 then determines which precoding matrix touse for determining the beamforming weights by processing the extractedmessage.

In some implementations, the receive data processor 860 and/or theprocessor 870 performs the link adaptation operations described herein.It should be appreciated that these operations may be performed incooperation with other components of FIG. 8 and/or by other componentsof FIG. 8 in some implementations.

A wireless node may include various components that perform functionsbased on signals that are transmitted by or received at the wirelessnode. For example, in some implementations, a wireless node comprises anantenna (e.g., coupled to transceiver) for transmitting and receivingsignals (e.g., comprising frames, etc.). As another example, in someimplementations, a wireless node comprises a user interface configured:to output an indication based on information received by a transceiverthrough the use of at least one transmission parameter and/or to provideinformation to be transmitted by a transceiver through the use of atleast one transmission parameter.

A wireless node as taught herein may communicate via one or morewireless communication links that are based on or otherwise support anysuitable wireless communication technology. For example, in some aspectsa wireless node may associate with a network such as a local areanetwork (e.g., a Wi-Fi network) or a wide area network. To this end, awireless node may support or otherwise use one or more of a variety ofwireless communication technologies, protocols, or standards such as,for example, Wi-Fi, WiMAX, CDMA, TDMA, OFDM, and OFDMA. Also, a wirelessnode may support or otherwise use one or more of a variety ofcorresponding modulation or multiplexing schemes. A wireless node maythus include appropriate components (e.g., air interfaces) to establishand communicate via one or more wireless communication links using theabove or other wireless communication technologies. For example, adevice may comprise a wireless transceiver with associated transmitterand receiver components that may include various components (e.g.,signal generators and signal processors) that facilitate communicationover a wireless medium.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of apparatuses (e.g., devices). For example,one or more aspects taught herein may be incorporated into a phone(e.g., a cellular phone), a personal data assistant (PDA), anentertainment device (e.g., a music or video device), a headset (e.g.,headphones, an earpiece, etc.), a microphone, a medical sensing device(e.g., a sensor such as a biometric sensor, a heart rate monitor, apedometer, an EKG device, a smart bandage, a vital signal monitor,etc.), a user I/O device (e.g., a watch, a remote control, a switch suchas a light switch, a keyboard, a mouse, etc.), an environment sensingdevice (e.g., a tire pressure monitor), a monitor that may receive datafrom the medical or environment sensing device, a computer, apoint-of-sale device, an entertainment device, a hearing aid, a set-topbox, a gaming device, or any other suitable device. The communicationdevices described herein may be used in any type of sensing application,such as for sensing automotive, athletic, and physiological (medical)responses. Any of the disclosed aspects of the disclosure may beimplemented in many different devices. For example, in addition tomedical applications as discussed above, the aspects of the disclosuremay be applied to health and fitness applications. Additionally, theaspects of the disclosure may be implemented in shoes for differenttypes of applications. There are other multitudes of applications thatmay incorporate any aspect of the disclosure as described herein.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of apparatuses (e.g., nodes). In someaspects, a node (e.g., a wireless node) implemented in accordance withthe teachings herein may comprise an access point or an access terminal.

For example, an access terminal may comprise, be implemented as, orknown as user equipment, a subscriber station, a subscriber unit, amobile station, a mobile, a mobile node, a remote station, a remoteterminal, a user terminal, a user agent, a user device, or some otherterminology. In some implementations an access terminal may comprise acellular telephone, a cordless telephone, a session initiation protocol(SIP) phone, a wireless local loop (WLL) station, a personal digitalassistant (PDA), a handheld device having wireless connectioncapability, or some other suitable processing device connected to awireless modem. Accordingly, one or more aspects taught herein may beincorporated into a phone (e.g., a cellular phone or smart phone), acomputer (e.g., a laptop), a portable communication device, a portablecomputing device (e.g., a personal data assistant), an entertainmentdevice (e.g., a music device, a video device, or a satellite radio), aglobal positioning system device, or any other suitable device that isconfigured to communicate via a wireless medium.

An access point may comprise, be implemented as, or known as a NodeB, aneNodeB, a radio network controller (RNC), a base station (BS), a radiobase station (RBS), a base station controller (BSC), a base transceiverstation (BTS), a transceiver function (TF), a radio transceiver, a radiorouter, a basic service set (BSS), an extended service set (ESS), amacro cell, a macro node, a Home eNB (HeNB), a femto cell, a femto node,a pico node, or some other similar terminology.

In some aspects a wireless node comprises an access device (e.g., anaccess point) for a communication system. Such an access deviceprovides, for example, connectivity to another network (e.g., a widearea network such as the Internet or a cellular network) via a wired orwireless communication link. Accordingly, the access device enablesanother device (e.g., a wireless station) to access the other network orsome other functionality. In addition, it should be appreciated that oneor both of the devices may be portable or, in some cases, relativelynon-portable. Also, it should be appreciated that a wireless node alsomay be capable of transmitting and/or receiving information in anon-wireless manner (e.g., via a wired connection) via an appropriatecommunication interface.

The teachings herein may be incorporated into various types ofcommunication systems and/or system components. In some aspects, theteachings herein may be employed in a multiple-access system capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., by specifying one or more of bandwidth, transmitpower, coding, interleaving, and so on). For example, the teachingsherein may be applied to any one or combinations of the followingtechnologies: Code Division Multiple Access (CDMA) systems,Multiple-Carrier CDMA (MCCDMA), Wideband CDMA (W-CDMA), High-SpeedPacket Access (HSPA, HSPA+) systems, Time Division Multiple Access(TDMA) systems, Frequency Division Multiple Access (FDMA) systems,Single-Carrier FDMA (SC-FDMA) systems, Orthogonal Frequency DivisionMultiple Access (OFDMA) systems, or other multiple access techniques. Awireless communication system employing the teachings herein may bedesigned to implement one or more standards, such as IS-95, cdma2000,IS-856, W-CDMA, TDSCDMA, and other standards. A CDMA network mayimplement a radio technology such as Universal Terrestrial Radio Access(UTRA), cdma2000, or some other technology. UTRA includes W-CDMA and LowChip Rate (LCR). The cdma2000 technology covers IS-2000, IS-95 andIS-856 standards. A TDMA network may implement a radio technology suchas Global System for Mobile Communications (GSM). An OFDMA network mayimplement a radio technology such as Evolved UTRA (E-UTRA), IEEE 802.11,IEEE 802.16, IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, and GSM arepart of Universal Mobile Telecommunication System (UMTS). The teachingsherein may be implemented in a 3GPP Long Term Evolution (LTE) system, anUltra-Mobile Broadband (UMB) system, and other types of systems. LTE isa release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE aredescribed in documents from an organization named “3rd GenerationPartnership Project” (3GPP), while cdma2000 is described in documentsfrom an organization named “3rd Generation Partnership Project 2”(3GPP2). Although certain aspects of the disclosure may be describedusing 3GPP terminology, it is to be understood that the teachings hereinmay be applied to 3GPP (e.g., Re199, Re15, Re16, Re17) technology, aswell as 3GPP2 (e.g., 1×RTT, 1×EV-DO Re10, RevA, RevB) technology andother technologies.

The components described herein may be implemented in a variety of ways.Referring to FIGS. 9-11, apparatuses 900, 1000, and 1100 are representedas a series of interrelated functional blocks that represent functionsimplemented by, for example, one or more integrated circuits (e.g., anASIC) or implemented in some other manner as taught herein. As discussedherein, an integrated circuit may include a processor, software, othercomponents, or some combination thereof.

The apparatuses 900, 1000, and 1100 includes one or more modules thatperform one or more of the functions described above with regard tovarious figures. For example, an ASIC for receiving a frame at a firstapparatus, wherein the frame comprises a request for at least onetransmission parameter and that further comprises identifiers of aplurality of apparatuses 902 may correspond to, for example, atransceiver as discussed herein. An ASIC for determining that the firstapparatus is identified by one of the identifiers 904 may correspond to,for example, a processing system as discussed herein. An ASIC fortransmitting the requested at least one transmission parameter as aresult of the determination 906 may correspond to, for example, atransceiver as discussed herein. An ASIC for receiving a null datapacket from a second apparatus that transmitted the frame comprising therequest and the identifiers 908 may correspond to, for example, atransceiver as discussed herein. An ASIC for determining the at leastone transmission parameter based on the received null data packet 910may correspond to, for example, a processing system as discussed herein.An ASIC for determining whether each apparatus of a plurality ofapparatuses has indicated that responses will be provided to requestsfor at least one transmission parameter 1002 may correspond to, forexample, a processing system as discussed herein. An ASIC fortransmitting a frame as a result of the determination, wherein the framecomprises a request for the at least one transmission parameter from theplurality of apparatuses and identifiers of the plurality of apparatuses1004 may correspond to, for example, a transceiver as discussed herein.An ASIC for receiving the at least one transmission parameter from theplurality of apparatuses as a result of transmitting the frame 1006 maycorrespond to, for example, a transceiver as discussed herein. An ASICfor using the received at least one transmission parameter to conduct atleast one transmission to the plurality of apparatuses 1008 maycorrespond to, for example, a transceiver as discussed herein. An ASICfor estimating at least one transmission parameter for SU beamformedtransmission based on a channel estimate for MU transmission by anapparatus 1102 may correspond to, for example, a processing system asdiscussed herein. An ASIC for generating a frame including the channelestimate and the at least one transmission parameter 1104 may correspondto, for example, a processing system as discussed herein. An ASIC fortransmitting the frame to the apparatus 1106 may correspond to, forexample, a transceiver as discussed herein. An ASIC for receiving a nulldata packet announcement (NDPA) frame with a compressed channel feedbacktype set to multi-user beamforming 1108 may correspond to, for example,a transceiver as discussed herein.

As noted above, in some aspects these components may be implemented viaappropriate processor components. These processor components may in someaspects be implemented, at least in part, using structure as taughtherein. In some aspects a processor may be configured to implement aportion or all of the functionality of one or more of these components.In some aspects, one or more of any components represented by dashedboxes are optional.

As noted above, the apparatuses 900, 1000, and 1100 each comprise one ormore integrated circuits in some implementations. For example, in someaspects a single integrated circuit implements the functionality of oneor more of the illustrated components, while in other aspects more thanone integrated circuit implements the functionality of one or more ofthe illustrated components.

In addition, the components and functions represented by FIGS. 9-11 aswell as other components and functions described herein, may beimplemented using any suitable means. Such means are implemented, atleast in part, using corresponding structure as taught herein. Forexample, the components described above in conjunction with the “ASICfor” components of FIGS. 9-11 correspond to similarly designated “meansfor” functionality. Thus, one or more of such means is implemented usingone or more of processor components, integrated circuits, or othersuitable structure as taught herein in some implementations.

Also, it should be understood that any reference to an element hereinusing a designation such as “first,” “second,” and so forth does notgenerally limit the quantity or order of those elements. Rather, thesedesignations are generally used herein as a convenient method ofdistinguishing between two or more elements or instances of an element.Thus, a reference to first and second elements does not mean that onlytwo elements may be employed there or that the first element mustprecede the second element in some manner. Also, unless stated otherwisea set of elements comprises one or more elements. In addition,terminology of the form “at least one of A, B, or C” or “one or more ofA, B, or C” or “at least one of the group consisting of A, B, and C”used in the description or the claims means “A or B or C or anycombination of these elements.” For example, this terminology mayinclude A, or B, or C, or A and B, or A and C, or A and B and C, or 2A,or 2B, or 2C, and so on.

Those of skill in the art understand that information and signals may berepresented using any of a variety of different technologies andtechniques. For example, any data, instructions, commands, information,signals, bits, symbols, and chips referenced throughout the abovedescription may be represented by voltages, currents, electromagneticwaves, magnetic fields or particles, optical fields or particles, or anycombination thereof.

Those of skill would further appreciate that any of the variousillustrative logical blocks, modules, processors, means, circuits, andalgorithm steps described in connection with the aspects disclosedherein may be implemented as electronic hardware (e.g., a digitalimplementation, an analog implementation, or a combination of the two,which may be designed using source coding or some other technique),various forms of program or design code incorporating instructions(which may be referred to herein, for convenience, as “software” or a“software module”), or combinations of both. To clearly illustrate thisinterchangeability of hardware and software, various illustrativecomponents, blocks, modules, circuits, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the aspects disclosed herein may be implementedwithin or performed by a processing system, an integrated circuit(“IC”), an access terminal, or an access point. A processing system maybe implemented using one or more ICs or may be implemented within an IC(e.g., as part of a system on a chip). An IC may comprise a generalpurpose processor, a digital signal processor (DSP), an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) or other programmable logic device, discrete gate or transistorlogic, discrete hardware components, electrical components, opticalcomponents, mechanical components, or any combination thereof designedto perform the functions described herein, and may execute codes orinstructions that reside within the IC, outside of the IC, or both. Ageneral purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

It is understood that any specific order or hierarchy of steps in anydisclosed process is an example of a sample approach. Based upon designpreferences, it is understood that the specific order or hierarchy ofsteps in the processes may be rearranged while remaining within thescope of the present disclosure. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

The steps of a method or algorithm described in connection with theaspects disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module (e.g., including executable instructions and relateddata) and other data may reside in a memory such as RAM memory, flashmemory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk,a removable disk, a CD-ROM, or any other form of computer-readablestorage medium known in the art. A sample storage medium may be coupledto a machine such as, for example, a computer/processor (which may bereferred to herein, for convenience, as a “processor”) such theprocessor can read information (e.g., code) from and write informationto the storage medium. A sample storage medium may be integral to theprocessor. The processor and the storage medium may reside in an ASIC.The ASIC may reside in user equipment. In the alternative, the processorand the storage medium may reside as discrete components in userequipment. Moreover, in some aspects any suitable computer-programproduct may comprise a computer-readable medium comprising codes (e.g.,executable by at least one computer) relating to one or more of theaspects of the disclosure. In some aspects a computer program productmay comprise packaging materials.

In one or more exemplary aspects, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by acomputer. By way of example, and not limitation, such computer-readablemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Thus, in some aspects computer readablemedium may comprise non-transitory computer readable medium (e.g.,tangible media). In addition, in some aspects computer readable mediummay comprise transitory computer readable medium (e.g., a signal).Combinations of the above should also be included within the scope ofcomputer-readable media.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining, and thelike. Also, “determining” may include receiving (e.g., receivinginformation), accessing (e.g., accessing data in a memory), and thelike. Also, “determining” may include resolving, selecting, choosing,establishing, and the like.

The previous description of the disclosed aspects is provided to enableany person skilled in the art to make or use the present disclosure.Various modifications to these aspects will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other aspects without departing from the scope of thedisclosure. Thus, the present disclosure is not intended to be limitedto the aspects shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

What is claimed is:
 1. An apparatus for wireless communication,comprising: a transceiver configured to receive a frame, wherein theframe comprises a request for at least one transmission parameter andfurther comprises identifiers of a plurality of apparatuses; and aprocessing system configured to determine that the apparatus isidentified by one of the identifiers, wherein the transceiver is furtherconfigured to transmit the requested at least one transmission parameteras a result of the determination.
 2. The apparatus of claim 1, wherein:the frame comprises a null data packet announcement (NDPA) frame; theidentifiers are included in station information (STA Info) fields of theNDPA frame; the request for at least one transmission parametercomprises an HT Control field with a modulation and coding schemerequest (MRQ) bit set to 1; the determination that the apparatus isidentified by one of the identifiers comprises determining that theapparatus is listed in an association identifier (AID) field of one ofthe STA Info fields; and the requested at least one transmissionparameter is transmitted via a modulation and coding scheme feedback(MFB) response.
 3. The apparatus of claim 2, wherein the at least onetransmission parameter comprises at least one of: bandwidth, number ofspatial streams, SNR, or type of coding.
 4. The apparatus of claim 2,wherein the MFB response is transmitted via a very high throughput (VHT)Compressed Beamforming frame.
 5. The apparatus of claim 1, wherein: thetransceiver is further configured to receive a null data packet from asecond apparatus that transmitted the frame comprising the request andthe identifiers; and the processing system is further configured todetermine the at least one transmission parameter based on the receivednull data packet.
 6. The apparatus of claim 5, wherein the determinationof the at least one transmission parameter comprises: generating anestimate of a channel between the apparatus and the second apparatusbased on the received null data packet; and generating the at least onetransmission parameter based on the estimate of the channel.
 7. A methodof wireless communication, comprising: receiving a frame at a firstapparatus, wherein the frame comprises a request for at least onetransmission parameter and further comprises identifiers of a pluralityof apparatuses; determining that the first apparatus is identified byone of the identifiers; and transmitting the requested at least onetransmission parameter as a result of the determination.
 8. The methodof claim 7, wherein: the frame comprises a null data packet announcement(NDPA) frame; the identifiers are included in station information (STAInfo) fields of the NDPA frame; the request for at least onetransmission parameter comprises an HT Control field with a modulationand coding scheme request (MRQ) bit set to 1; the determination that thefirst apparatus is identified by one of the identifiers comprisesdetermining that the first apparatus is listed in an associationidentifier (AID) field of one of the STA Info fields; and the requestedat least one transmission parameter is transmitted via a modulation andcoding scheme feedback (MFB) response.
 9. The method of claim 8, whereinthe at least one transmission parameter comprises at least one of:bandwidth, number of spatial streams, SNR, or type of coding.
 10. Themethod of claim 8, wherein the MFB response is transmitted via a veryhigh throughput (VHT) Compressed Beamforming frame.
 11. The method ofclaim 7, further comprising: receiving a null data packet from a secondapparatus that transmitted the frame comprising the request and theidentifiers; and determining the at least one transmission parameterbased on the received null data packet.
 12. The method of claim 11,wherein the determination of the at least one transmission parametercomprises: generating an estimate of a channel between the firstapparatus and the second apparatus based on the received null datapacket; and generating the at least one transmission parameter based onthe estimate of the channel.
 13. An apparatus for wirelesscommunication, comprising: means for receiving a frame, wherein theframe comprises a request for at least one transmission parameter andfurther comprises identifiers of a plurality of apparatuses; means fordetermining that the apparatus is identified by one of the identifiers;and means for transmitting the requested at least one transmissionparameter as a result of the determination.
 14. The apparatus of claim13, wherein: the frame comprises a null data packet announcement (NDPA)frame; the identifiers are included in station information (STA Info)fields of the NDPA frame; the request for at least one transmissionparameter comprises an HT Control field with a modulation and codingscheme request (MRQ) bit set to 1; the determination that the apparatusis identified by one of the identifiers comprises determining that theapparatus is listed in an association identifier (AID) field of one ofthe STA Info fields; and the requested at least one transmissionparameter is transmitted via a modulation and coding scheme feedback(MFB) response.
 15. The apparatus of claim 14, wherein the at least onetransmission parameter comprises at least one of: bandwidth, number ofspatial streams, SNR, or type of coding.
 16. The apparatus of claim 14,wherein the MFB response is transmitted via a very high throughput (VHT)Compressed Beamforming frame.
 17. The apparatus of claim 13, furthercomprising: means for receiving a null data packet from a secondapparatus that transmitted the frame comprising the request and theidentifiers; and means for determining the at least one transmissionparameter based on the received null data packet.
 18. The apparatus ofclaim 17, wherein the determination of the at least one transmissionparameter comprises: generating an estimate of a channel between theapparatus and the second apparatus based on the received null datapacket; and generating the at least one transmission parameter based onthe estimate of the channel.
 19. A computer-program product for wirelesscommunication, comprising: computer-readable storage medium comprisingcodes executable to: receive a frame at a first apparatus, wherein theframe comprises a request for at least one transmission parameter andfurther comprises identifiers of a plurality of apparatuses; determinethat the first apparatus is identified by one of the identifiers; andtransmit the requested at least one transmission parameter as a resultof the determination.
 20. A wireless node, comprising: an antenna; atransceiver configured to receive a frame via the antenna, wherein theframe comprises a request for at least one transmission parameter andfurther comprises identifiers of a plurality of wireless nodes; and aprocessing system configured to determine that the wireless node isidentified by one of the identifiers, wherein the transceiver is furtherconfigured to transmit the requested at least one transmission parameteras a result of the determination.